Electrical ground detector



Nov. 24, 1953 Filed Dec. 22, 1949 us I126,

H 50 1.7a I f 21 [l 17 0 W 25 15 *1: ,17a l: D 15 4l 42 INVENTOR.

ains 5% AWL Patented Nov. 24, 1953 UNITED STATES PATENT OFFICE.

2 Claims.

This invention relates to an electrical ground detector.

A general object of the invention is to provide a safety ground detector which will indicate the grounding of an electrical current.

Another object is to provide a safety ground detector which has been designed particularly for use in hospital operating rooms or industrial plants and which includes an audible or visible signal which will be rendered active when the electrical conductor in said room or plant has become grounded and the leakage is sufficient to cause muscular reflex in a human body when the current is conducted through the body to the round.

Still another object is to provide a resistor to limit the flow of electric energy which might pass through the body of one or more persons becoming grounded, said current energy measuring less than 3'75 microamperes, eliminating danger of electric shock, muscular reflex and electric sparks, to protect against the ignition of explosive gases when a secondary wire from the isola' tion transformer becomes grounded.

A further object of the invention is to provide a sensitive detector of the character described which will eliminate the accumulation of negative and positive static electricity on ungrounded conductors, which prevents the possibility of the danger of explosions due to static discharges in hazardous places such as hospital operating rooms, chemical and petroleum refineries and similar places where explosive gases are present.

Other objects and advantages will be apparent from the following specification which is illu..-

trated by the accompanying drawing, wherein:

The figure is a diagrammatic view of the detector.

Referring more particularly to the drawing the numerals I, Ia are the electrical conductors lead- 1 ing from the source of energy.

A transformer, as 2, must be employed to deliver the electrical current from conductors I, la to the electrical conductors 3, 4 which lead to the equipment to be used in a hospital operating room Or in an industrial plant.

The ground detector is connected into the circuit through the ungrounded conductors 3, 4. As shown, there are suitable resistor units 5, 6 connected into the respective conductors 3, 4 and also connected with the corresponding rectifiers I and 8.

Current may then flow through resistor 9 to relay Ill and thence to ground II. The rectifiers I, 8 produce direct current rectifier impulses to actuate relay Ill. These rectifiers are connected into a common point by an electrical conductor I2 so that current can flow through these blocking rectifier elements toward the common point only. Conductor Illa connects with conductor I8 and conductor 3 and leads to resistor 38 thence through the resistor to the fixed contact I3 and hand electrode 66. There is also a moveable contact Id which, when closed with contact I3, will form a circuit from the common point in In to ground I5, ground ll, relay I0, through resistor 9 and conductor 92. This, in turn, energizes relay m. The purpose is to test light signals and audible signal.

There is also a fixed contact I5, and the moveable contact It may be closed with this fixed contact I6.

The moveable contact, as shown, is of the selfcentering type and may be moved into closed position with either contact I3 or IE.

There are the electrical conductors I1, I8 which lead from the respective conductors 3 and 4. The conductor I'I terminates in a fixed contact I9, and opposing this fixed contact I9 there is a fixed contact 20.

The conductor I8 terminates in a moveable contact 2| which may be closed with either of the contacts IE or 2D.

The relay iii is positioned to actuate the moveable contact 2 I, and when it is energized, as above explained, it will move contact 2| from contact I9 into closed position with contact 20.

Incorporated into conductor I! there is a light globe 22, in the present instance green, and also, preferably, a'resisto'r 23. The resistor 23 is provided to reduce voltage of the filaments of lights 22 and 4| and increase the life of the filaments. Of course, other types of electrical signal may be employed. When the contacts I9, 2| are closed the signals 22 and M will be energized. When contacts I4, I3 are closed and relay I0 energized and contact 2I moved from contact I9 and closed with contact 2t, as above explained, the signals 22 and 4| will be extinguished, or rendered inactive.

Leading from contact 20 and connected into conductor I"! there is an electrical conductor I'Ia, and in this conductor there are light globes 24 and 42, in the present instance red and green, or other selected electrical signals. These signals will be energized when contacts 2|, 2!! are closed and signals 22 and Al extinguished.

An audible signal may also be provided to take the place of, or to operate in conjunction with, the signal 24. In the present illustration, this is shown as an alarm bell 25, which is in an electrical. conductor 26 leading from conductor [1 and terminating in a fixed contact 21 which opposes and is spaced from a fixed contact 28. An electrical conductor 29 connects contacts I6 and 28.

There is a relay 3% in the electrical conductor 3|, which conductor leads from conductor IT to conductor 29, and when contacts 20, 2| are closed the current flows from conductor Ha to .contact 32, which is in contact with contact point 2''! and thence through conductor 26 to operate signal 25. This contact 32 is moveable and is connected into conductor lia so as to electrically connect the conductors 26, 29, alternatively, with conductor Ila. When contacts I4 and 1.6 are closed,

the relay 30 then becomes energized and closes contacts 32, 28, thus (is-energizing signal 25, and upon closing switch It with contact point 13 signal 24 is energized and signal 22 is de-energized.

The signals 24, 25 remain active until the moveable contact M, which is self-centering, assumes itsnormal, open position. Upon contact ,I 4 moving to open position, the contact between the moveable contact 32 and the fixed contact 27 will energized upon closing of the switches l4, l3. 2.

When this contact is broken, the signals 24, 25 and 42 become inoperative and the signal 22 and 4.1 is re-energized.

The conductors I, la are provided with overcurrent protecting devices 33, 34 which are provided to protect the primary circuit of the isolation transformer 2 from over-current supply, and incorporated into the secondary conductors "3, 4 there are over-current protecting devices 35, 3.6 to similarly protect the secondary winding. These over-current protecting devices may be ordinary fuse plugs, if desired, or similar devices.

During the normal operation of the protected equipment the green light 22 will be eliminated or be active, and it may be here stated that the switches 2|, 32 are normally in the position indicated in the drawing, that is, connected with the respective contacts [9, 21, and so maintained by the customary spring or similar device for such purpose.

When pulsating, direct current passes through the body of one or more persons from the line 3 or 4, such persons will be protected against electric shock through the resistor 9 and the relay winding ill, to the ground as the circuit will pass only sufficient current to actuate said relay and give warning signals, this current being not more than 400 microamperes.

Should an accidental ground occur on conductor 3 or 4 current will pass through resistor 9 and relay Hi to ground II, and the current from ground H wil1 pass back to conductor 3 or 4, whichever one becomes grounded. This will operate relay [0, and switch 2i will be moved into contact with contact 20, and the green light 22 will be extinguished and current will be conducted through lla to illuminate the red light 24 and, the switch 32 still being closed with point 21, current will also flow through the conductor 26 to render the signal 25 active. There is a .foot electrode 39 located outside the operating room, are for the purpose of making a momentary test of the conductivity of personnel before,

entering the operating room. A red light indicating danger, signifies no current is flowing through the body from hand electrode 46 to foot electrode 39. When current flows through the body from electrode 40 to 39, a circuit is established from the common point between rectifiers 1 and '8, through the resistance 9, the relay it, ground ll, ground l5, foot electrode through the body to hand electrode 40, through resistance 38 and conductor I2c to conductor I13 and ungrounded conductor 3. Establishment of this circuit causes energization of the relay it which lie-energizes the red light 4! and energizes the green light '42, and. the alarm signal 25, thus "Hating current is flowing through the body hand electrode Mi to foot electrode 39. it also enables the electro-static potential which accumulate on the body of a person to how to the grounded terrazzo iioor in the operating room through the conductive soles of shoes required by hospital personnel and surgeons to equalize the electro-static potential that may form on the body which would prevent the possi bility of forming a spark or are which could i';- nite explosive, anesthetic gases.

In order to silence the audible the operator throw switch it into con act wit.

contact which will relay thus throwing the switch 32 into contact with point thereby silencing the signal. The id, being a self-centering switch, will imin ately move to open position, and points 31; it will remain in. contact due to the holding coil action of the relay 39. This indicates that conductor or t is grounded, and this defect should be removed by the electrician. and when removed the current flowing to the ground it is stopped, and the relay [2 tie-en,"

thereupon switch 2! will move into contact with point i9 and the green light 22 and red light H illuminated. At the same time, current through conductor 29, iii is broken, and the relay 30 is deenergized, and switch 32 moves to normal posi tion into contact with contact point 21.

..t may be here stated that direct current may be used, and the circuits may be singleor multi-phase alternating current circuits.

What 'I claim is:

l. A system for use in areas wl'iere explosive gases are present comprising an isolation transformer, a, plurality of ungrounded conductors connected to the secondary of the transformer and adapted for supplying energy to electrical equipment, blocking rectifier elements so con-'- nected between each of said conductors and common point that current can flow through said elements toward the common point only, said common point being connected to ground through a resistance; said resistance being sufliciently high to limit the current passing through a person, who may come in contact with one of said ungrounded conductors, to an amount insufficient to cause muscular reflex or electric shock, said resistance also being sufficiently high to eliminate the occurrence of an explosion producing electric spark should one of the ungrounded conductors accidentally become grounded, a relay coil connected between said common point and said ground and in series with said resistance, and signal means controlled by the relay coil for indicating the presence of said current.

2. A system as set forth in claim 1, said signal means including a signal device, conductors normally connecting the signal device across said ungrounded conductors, a warning signal, conductors for connecting the warning signal across said ungrounded conductors, and means associated with said relay coil for rendering said first mentioned signal device inactive and for rendering said warning signal active when one of said ungrounded conductors becomes accidentally grounded.

HERMAN A. HOOD.

References Cited in the file of this patent UNITED STATES PATENTS 

